A number of manufacturing processes make use of particulate thermoplastic polymer compositions, commonly known in the art as “powder compositions.” Additive manufacturing (AM, also known as “three-dimensional” or “3D” printing) is a process for the manufacture of three-dimensional objects by formation of multiple fused layers. AM methods using powder compositions include powder bed fusing. In powder bed fusing, thermal energy selectively fuses regions of a powder bed. In particular, selective laser sintering (SLS) is a powder bed fusion process using one or more lasers to fuse powdered thermoplastic polymers into the desired three-dimensional shape. In powder coating, the powder composition is applied to a surface, for example electrostatically, and then heated, allowing the particles to coalesce and form a film. Powder compositions have also been compression molded to form articles.
Despite their long use, there remains a need in the art for optimized powder properties, in particular optimized shape and size of the polymer particulates. Ease of particle handling has driven practitioners to larger particle sizes. However, larger particle sizes coalesce more slowly during the sintering process. Particle size can also affect the porosity of the final product. In the manufacturing of parts by the sintering of particles, the mechanical properties of the final article can be deficient compared to the same article formed of the same material by methods such as injection molding. This discrepancy in properties is typically attributable to the increased porosity of the sintered part resulting from suboptimal packing and coalescence of the particles.
It can further be difficult to use amorphous thermoplastic polymers in these processes, particularly in powder bed fusing, because the amorphous polymers do not have a sharp melting point. This property causes the applied thermal energy source (e.g., a laser beam) to be dissipated into the regions surrounding the location where the energy beam strikes the bed. This undesired dissipation of thermal energy can cause unstable processing as well as poor feature resolution in the intended three-dimensional articles being produced.
Therefore, there is a need in the art for powder compositions having optimized size and shape characteristics. It would be a further advantage if such compositions provided improved processing of amorphous polymers.